1. Field of the Invention
In one of its aspects, the present invention relates to an endovascular prosthesis. In another of its aspects, the present invention relates to a method of treating an aneurysm in a patient.
2. Brief Description of the Prior Art
As is known in the art, an aneurysm is an abnormal bulging outward in the wall of an artery. In some cases, the bulging may be in the form of a smooth bulge outward in all directions from the arteryxe2x80x94this is known as a xe2x80x9cfusiform aneurysmxe2x80x9d. In other cases, the bulging may be in the form of a sac arising from an arterial branching point or from one side of the arteryxe2x80x94this is known as a xe2x80x9csaccular aneurysmxe2x80x9d.
While aneurysms can occur in any artery of the body, it is usually those which occur in the brain which lead to the occurrence of a stroke. Most saccular aneurysms which occur in the brain have a neck which extends from the cerebral blood vessel and broadens into a pouch which projects away from the vessel.
The problems caused by such aneurysms can occur in several different ways. For example, if the aneurysm ruptures, blood enters the brain or the subarachnoid space (i.e., the space closely surrounding the brain)xe2x80x94the latter is known as aneurysmal subarachnoid hemorrhage. This followed by one or more of the following symptoms: nausea, vomiting, double vision, neck stiffness and loss of consciousness. Aneurysmal subarachnoid hemorrhage is an emergency medical condition requiring immediate treatment. Indeed, 10-15% of patients with the condition die before reaching the hospital for treatment. More than 50% of patients with the condition will die within the first thirty days after the hemorrhage. Of those patients who survive, approximately half will suffer a permanent stroke. Some of these strokes occur one to two weeks after the hemorrhage itself from vasospasm in cerebral vessels induced by the subarachnoid hemorrhage. Aneurysms also can cause problems which are not related to bleeding although this is less common. For example, an aneurysm can form a blood clot within itself which can break away from the aneurysm and be carried downstream where it has the potential to obstruct an arterial branch causing a stroke. Further, the aneurysm can also press against nerves (this has the potential of resulting in paralysis or abnormal sensation of one eye or of the face) or the adjacent brain (this has the potential of resulting in seizures).
Given the potentially fatal consequences of the aneurysms, particularly brain aneurysms, the art has addressed treatment of aneurysms using various approaches.
Generally, aneurysms may be treated from outside the blood vessels using surgical techniques or from the inside using endovascular techniques (the latter falls under the broad heading of interventional (i.e., non-surgical) techniques).
Surgical techniques usually involve a craniotomy requiring creation of an opening in the skull of the patient through which the surgeon can insert instruments to operate directly on the brain. In one approach, the brain is retracted to expose the vessels from which the aneurysm arises and then the surgeon places a clip across the neck of the aneurysm thereby preventing arterial blood from entering the aneurysm. If there is a clot in the aneurysm, the clip also prevents the clot from entering the artery and obviates the occurrence of a stroke. Upon correct placement of the clip the aneurysm will be obliterated in a matter of minutes. Surgical techniques are the most common treatment for aneurysms. Unfortunately, surgical techniques for treating these conditions are regarded as major surgery involving high risk to the patient and necessitate that the patient have strength even to have a chance to survive the procedure.
As discussed above, endovascular techniques are non-surgical techniques and are typically performed in an angiography suite using a catheter delivery system. Specifically, known endovascular techniques involve using the catheter delivery system to pack the aneurysm with a material which prevents arterial blood from entering the aneurysmxe2x80x94this technique is broadly known as embolization. One example of such an approach is the Guglielmi Detachable Coil which involves intra-aneurysmal occlusion of the aneurysm via a system which utilizes a platinum coil attached to a stainless steel delivery wire and electrolytic detachment. Thus, once the platinum coil has been placed in the aneurysm, it is detached from the stainless steel delivery wire by electrolytic dissolution. Specifically, the patient""s blood and the saline infusate act as the conductive solutions. The anode is the stainless steel delivery wire and the cathode is the ground needle which is placed in the patient""s groin. Once current is transmitted through the stainless steel delivery wire, electrolytic dissolution will occur in the uninsulated section of the stainless steel detachment zone just proximal to the platinum coil (the platinum coil is of course unaffected by electrolysis). Other approaches involve the use of materials such as cellulose acetate polymer to fill the aneurysm sac. While these endovascular approaches are an advance in the art, they are disadvantageous. Specifically, the risks of these endovascular approaches include rupturing the aneurysm during the procedure or causing a stroke due to distal embolization of the device or clot from the aneurysm. Additionally, concern exists regarding the long term results of endovascular aneurysm obliteration using these techniques. Specifically, there is evidence of intra-aneurysmal rearrangement of the packing material and reappearance of the aneurysm on follow-up angiography.
One particular type of brain aneurysm which has proven to be very difficult to treat, particularly using the surgical clipping or endovascular embolization techniques discussed above occurs at the distal basilar artery. This type of aneurysm is a weak outpouching, usually located at the terminal bifurcation of the basilar artery. Successful treatment of this type of aneurysm is very difficult due, at least in part, to the imperative requirement that all the brainstem perforating vessels be spared during surgical clip placement.
Unfortunately, there are occasions when the size, shape and/or location of an aneurysm make both surgical clipping and endovascular embolization not possible for a particular patient. Generally, the prognosis for such patients is not good.
Accordingly, while the prior art has made advances in the area of treatment of aneurysms, there is still room for improvement, particularly in endovascular embolization since it is such an attractive alternative to major surgery. Specifically, it would be desirable to have an endovascular prosthesis which could be used in the embolization of aneurysms which are difficult or not possible to treat otherwise. It would be further desirable if such an endovascular prosthesis could be used to treat aneurysms currently treated endovascularly while mitigating or obviating the disadvantages associated with current endovascular embolization techniques.
It is an object of the present invention to provide a novel endovascular prosthesis which obviates or mitigates at least one of the above-mentioned disadvantages of the prior art.
It is another object of the present invention to provide a novel method for endovascular blocking an aneurysmal opening which obviates or mitigates at least one of the above-mentioned disadvantages of the prior art.
Accordingly, in one of its aspects, the present invention relates to an expandable endovascular prosthesis comprising:
a body having a proximal end and a distal end;
a first expandable portion disposed between the proximal end and the distal end, the first expandable portion being expandable from a first, unexpanded state to a second, expanded state with a radially outward force thereon to urge the first expandable portion against a vascular lumen; and
a second expandable portion attached to the first expandable portion;
the second expandable portion being expandable upon expansion of the first expandable portion.
In yet another of its aspects, the present invention relates to a method for endovascular blocking of an aneurysmal opening with a prosthesis comprising: a body having a proximal end and a distal end, a first expandable portion disposed between the proximal end and the distal end, the first expandable portion being expandable from a first, unexpanded state to a second, expanded state with a radially outward force thereon to urge the first expandable portion against a vascular lumen, and a second expandable portion attached to the first expandable portion; the second expandable portion being expandable upon expansion of the first expandable portion, the method comprising the steps of:
disposing the prosthesis on a catheter;
inserting the prosthesis and catheter within a body passageway by catheterization of the body passageway;
translating the prosthesis and catheter to a target vascular lumen at which the aneurysm opening is located;
exerting a radially outward expansive force on the first expandable portion such that the tubular first expandable portion is urged against the target body passageway;
causing expansion of the first expandable portion to expand the second expandable portion;
urging the second expandable portion against the aneurysmal opening thereby blocking the aneurysmal opening.
Thus, the present inventors have discovered a novel endovascular prosthesis having the characteristic of a first expandable portion which, when expanded, causes a second expandable portion (connected to the first expandable) to expand. For example, if the first expandable portion is made of a plastically deformable material (e.g., stainless steel), upon expansion, the first expandable portion will plastically deform. Such expansion will expand the second expandable portion. As will be developed hereinbelow, an endovascular prosthesis having these features is desirable, particularly in the treatment of aneurysms.
Preferably, and as will be further developed hereinbelow, the first expandable portion is generally tubular in structure. Indeed, throughout this specification, reference will be made to a first expandable portion which is generally tubular in structure. However, such reference is for illustrative purposes only and those of skill in the art will recognize that it is possible to utilize a non-tubular structure (e.g., a claw-like design which opens upon expansion) as the first expandable portion.
In International Publication Number WO 99/40873 [Marotta et al. (Marotta)], published Aug. 19, 1999, there is taught a novel endovascular approach useful in blocking of an aneurysmal opening, particularly those in saccular aneurysms, leading to obliteration of the aneurysm. The approach is truly endovascular in that, with the endovascular prosthesis taught by Marotta, there is no requirement to pack the aneurysmal sac with a material (e.g., such is used with the Guglielmi Detachable Coil). Rather, the endovascular prosthesis taught by Marotta operates on the basis that it serves to block the opening to the aneurysmal sac thereby obviating the need for packing material. Thus, the endovascular prosthesis taught by Marotta is an important advance in the art since it obviates or mitigates many of the disadvantages of the prior art. The endovascular prosthesis taught by Marotta comprises a leaf portion capable of being urged against the opening of the aneurysm thereby closing the aneurysm. In the endovascular prosthesis taught by Marotta, the leaf portion is attached to, and independently moveable with respect to, a body comprising at least one expandable portion. The expandable portion is expandable from a first, unexpanded state to a second, expanded state with a radially outward force thereon. Thus, the body serves the general purpose of fixing the endovascular prosthesis in place at a target body passageway or vascular lumen in the vicinity at which the aneurysmal opening is located and the leaf portion serves the purpose of sealing the aneurysmal opening thereby leading to obliteration of the aneurysm. Thus, as taught by Marotta, the leaf portion functions and is moveable independently of the body of the endovascular prosthesis.
While the endovascular prosthesis taught by Marotta is a significant advance in the art, there is still room for improvement. Specifically, in the preferred embodiment of the endovascular prosthesis taught by Marotta, once the device is deployed and the leaf portion is properly positioned, the surface area of the leaf portion is delimited by the surface area of the tube from which the leaf portion was cut. While this may not be a problem in most instances, there are occasions where the aneurysmal opening is sufficiently large that there exists a real possibility that the leaf portion will not completely close off the aneurysmal opening. On the other hand, if one attempts to increase the size of the leaf portion by cutting it from a larger diameter tube, the diameter of the prosthesis increases which can make it more difficult to navigate into the correct position and to use with conventional delivery devices.
Thus, the present inventors have discovered a novel approach which allows for designing the body of the prosthesis to have a conventional tube diameter while having an expandable portion which expands in response to expansion of the body. Thus, in the present endovascular prosthesis, the body has a proximal end and distal end. Disposed between the proximal end and the distal end, there are at least two expandable portions connected to one another. The first expandable portion is expandable from a first, unexpanded state to a second, expanded state with a radially outward force thereon. The second expandable portion is attached to the first expandable portion and is expandable upon expansion of the first expandable portionxe2x80x94i.e., the means used to expand the first expandable portion does not directly expand the second expandable portion.
The body of the present endovascular prosthesis has a generally longitudinal axis and is flexible. In a preferred embodiment, the second expandable portion is independently moveable between at least a first position and a second position with respect to the body, expanded or unexpanded. Thus, in the first position, the distal end and the proximal end of the body (including the first expandable portion) are aligned with the second expandable portion. In the second position, while securing the distal end and the proximal end of the body, the second expandable portion maintains a degree of independent movement. In this manner, the second expandable portion is xe2x80x9cindependently moveablexe2x80x9d with respect to the body. In one embodiment, it is preferred that this independent movement is achieved by disposing the second expandable portion such that it may pivot with respect to the remainder of the endovascular prosthesis. It should be understood that, while the second expandable portion may be independently moveable with respect to the body, the final alignment of the distal end, the proximal end and second expandable portion (i.e., the alignment after blockage of the aneurysmal opening) is not particularly restricted and depends on factors such as the size and location of the aneurysm and the anatomy of the particular patient. The key point of this preferred embodiment is that the second expandable portion is capable of being independently moved with respect to the body.
The present endovascular prosthesis is believed to be particularly useful in the treatment of aneurysms such as those described hereinabove and is therefore believed to provide a significant alternative to the conventional surgical techniques described hereinabove. Additionally, it is envisaged that the present endovascular prosthesis may be used in the treatment of certain aneurysms which are diagnosed as being inoperable. The present endovascular prosthesis also is believed to provide a significant advantage of current endovascular approaches such as the Guglielmi Detachable Coil described hereinabove. Specifically, since the present endovascular prosthesis does not rely on insertion into the aneurysm of a metal packing material (e.g., platinum coil), the risk of rupturing the aneurysm is mitigated as is the risk of intra-aneurysmal rearrangement of the metal packing material and subsequent reappearance of the aneurysm.